The worm is spreading rapidly. Managed services firm MessageLabs had blocked Sobig-F 36,227 times since spotting it yesterday.

We're getting sick of saying this, but Sobig-F is a Windows-only menace. Mac, Linux, OS/2 and Unix users are immune.

For Windows users it's the now familiar routine of updating viral software, blocking executables at the gateway and crossing their fingers that the current viral plague will subside.

A substantial number of firms are beginning to question whether this approach is appropriate given the current onslaught of malicious code.

Firms like MessageLabs and Avecho.com argue that the only sensible place to block malicious code is before it reaches users whilst a new generation of behaviour blocking firms are coming forward with technology to lock down Windows PCs. ®